Milk is an important source of dietary calcium. Calcium, the most abundant mineral in body, is a major constituent of bone and teeth. This mineral also plays an important role in several physiological systems. Calcium is important for healthy bone and tooth development in the young and an adequate intake is essential. Calcium status may also be a factor in the development of osteoporosis in elderly people.
Since the body does not produce minerals, it is totally dependent on an external supply of calcium, nutritional or supplementary. The importance of adequate calcium intake is recognized during the whole life of the human being. In 1994, the NIH Consensus Development Panel revised recommended daily allowances for calcium intake for each age group from 800-1200 mg per day to 1500 mg per day.
It has been suggested that calcium in the association with caseins may improve absorption in the gastrointestinal tract. Also it has been found that organic acids salts of calcium are more bioavailable in general than the inorganic salts. Calcium citrate has advantages over other calcium salts for use in fortified foods because of high bioavailability. Calcium citrate, as opposed to calcium in general, has only a marginal effect of interfering with the absorption of other minerals, especially iron. Also, long-term calcium supplementation can reduce with calcium citrate the risk on the formation of kidney and urinary stones since citrate ions are inhibitors for crystallization of stone-forming calcium salts.
Addition of calcium to milk is a very significant problem. Firstly, if we use highly soluble sources of calcium (calcium chloride, etc.) high level of soluble calcium leads to protein coagulation during temperature treatment even at pasteurization temperature. Secondly, slightly soluble sources of calcium will not have destabilization of protein micelles but will precipitate rapidly. Accordingly, the solubility of the calcium sources has to be balanced within a very small range of solubility. Also, very fine forms of colloidal calcium have to be formed in milk in order not to significantly change the ratio between free and bonded calcium. In this case, the order of addition can have significant influence on calcium metastable compounds formation. Another factor which must be considered is the pH of milk with supplements because of it changing during the temperature treatment.
It would be highly desirable to have a calcium source to fortify milk, casein or whey containing beverages and other dairy based products without coagulation and sedimentation, with improved palatability, and without bitterness or off-flavor.